Actuator circuit for electromagnetic devices



B. B. DAIEN 3,265,938

ACTUATOR CIRCUIT FOR ELECTROMAGNETIC DEVICES Aug. 9, 1966 Filed Jan. 17, 1964 NA M M 8 2 F4 B N\ 3,265,938 ACTUATOR CIRCUIT FOR ELECTROMAGNETIC DEVICES Bernard B. Daien, Sutfern, N.Y., assignor to Automatic Switch Company, Florham Park, N.J., a corporation of v New York Filed Jan. 17, 1964, Ser. No. 338,415 1 Claim. (Cl. 317-1555) This invention relates to electromagnetic devices of the .type in which the movement of an armature is controlled by current flowing in a winding. More particularly, the. invention relates to an electric circuit for controlling the actuation of such devices.

In these electromagnetic devices, an example of which is a solenoid, an air gap is present in the magnetic circuit of the device when the winding is deenergized. Upon energizationof the winding, the armature or core moves in a direction which reduces the air gap. This movement continues until the armature reaches a seated position.

. When voltage is initially applied to the winding, the force exerted upon the armature tending to move it toward its seated position is relatively small due to the presence of a maximum air gap. As the air gap decreases, the force on the armature increases. When the armature reaches its seated position, the force on it is a maximum since the air gap is zero or nearly so. In fact, this force is ordinarily much greater than necessary to maintain the armature in its seated condition. It may be seen, therefore, that under the circumstances described above, the force on an armature is least when ideally it should be greatest, and the force is a maximum when only a relatively small force is necessary and desirable.

To alleviate this undesirable situation, it has been suggested in the past that a relatively large current be supplied to the winding to initiate movement of the armature, and that at the time, or just before, the armature seats, the current to the winding be reduced to a value just sufficient to maintain the armature in its seated condition. One scheme for achieving this result involves providing a resistor in series with the winding, and means for short-ci-rcuiting the resistor during the initial application of voltage to the winding. Consequently, full line voltage is initially applied to the winding, but thereafter, when the resistor is back in the circuit, a reduced voltage is applied to the winding. This arrangement has proven less than satisfactory in certain types of installations. One reason is that the efiiciency of this arrangement is very low since when the resistor is in the circuit, it dissipates a great amount of power in the form of heat. Another consideration is that With this arrangement the high power input at the instant the line switch is closed must be supplied by the source. Since the initial power required by the solenoid or like device may be five to ten times the steady-state value (when the armature is seated), the power source must be capable of handling this temporarily increased power demand.

It is a general object of the present invention to provide an actuating circuit for temporarily applying a much higher than normal voltage to the winding of an electromagnetic device of the type described, in order to exert a large initial force on the armature, withoutthe disadvantages attendant to the use of other schemes for this purpose.

It is a more specific object to provide such an actuating circuit offering high efiiciency and little power dissipation through heat loss, and in which relatively small components can be used because so little power is dissipated.

It is another object of the invention to provide such an actuating circuit in which the power source is required United States Patent 3,265,938 Patented August 9, 1966 to supply only the normal steady-state voltage necessary to maintain the armature in seated condition.

It is still another object of the invention to provide such an actuating circuit capable of frequent cycling.

It is a further object of the invention to provide such an actuating circuit having no contacts, other than the line switch for initiating operation, whereby the circuit is well suited for use in an explosive atmosphere.

To achieve these objects, the present invention provides an actuating circuit including a capacitor which is charged by a small amount of current from the power source. At the appropriate time, the capacitor discharges through the winding of the device being controlled, thereby applying a large voltage pulse to the winding and producing a large force on the armature. Flow of current from the capacitor to the winding is controlled by a solid state component.

A means is provided for conditioning the solid state component to conduct at the instant voltage from the power source is applied to the winding. Thereafter, the solid state component is automatically turned olf and the capacitor becomes recharged in preparation for the next cycle during which the electromagnet device is to be actuated.

Other objects and advantages of the invention will be apparent from the following detailed description of the invention, in which reference is made to the accompanying drawing.

The figure is a schematic representation of an actuating circuit chosen to illustrate the present invention.

The circuit illustrated is intended to control the actuation of a solenoid, or other electromagnetic device, having a main winding 10. The circuit is supplied from an alternating current power source through a transformer 11. The transformer has a primary 12 and two secondary windings 13 and 14. The secondary 13 is adapted to supply the normal or steady-state operating voltage of the winding 10 through a full-wave rectifier .15. Thus, the secondary 13 provides just enough current to the winding 10 to maintain the armature of the solenoid in seated condition. A line switch 16 controls the energization and deenergization of the winding 10. Connected in parallel with the winding 10 is a capacitor 17' which is charged constantly by the output of the rectifier 15. When the switch 16 is closed, the capacitor 17 discharge-s through the winding 10 and thereby insures that a voltage pulse is applied to the winding 10 regardless of the absolute value of the voltage of the power source at the instant the switch 16 is closed.

The solenoid winding 10 is connected in series with two other important elements of the present circuit. These are a capacitor 20, and a' silicon controlled rectifier 21 (hereinafter sometimes referred to as SCR) which is the solid state switching component of the present circuit. The secondary 14 of the transformer 11 is connected across the capacitor 20 and charges the latter through a halfwave rectifier 22 and a resistor 23. The resistor limits the amplitude of the charging current into the capacitor 20. The secondary 14 supplies a voltage higher than the normal operating voltage of the winding 10, i.e., higher than the voltage supplied by the secondary 13. Normally, the S'CR 21 does not conduct current thereby giving the capacitor 20 an opportunity to become charged. This capacitor will remain charged as long as the SCR remains non-conducting. Y

The gate 24 of the SCR is connected to a control winding 25. The control winding is inductively coupled to the main winding 10 so that when a voltage is applied to the polarity of the SCR must be such, at the moment voltage is applied to its gate, that the SCR is conditioned to fire. When the polarity of the SCR is reversed, it will not fire regardless of what voltage is applied to its gate.

The operation of the actuator circuit is as follows:

When the switch 16 is closed, a voltage is applied to the winding by virtue of the capacitor 17 which discharges through it. This voltage induces a voltage in the control winding 25. The induced voltage is applied to the gate 24 of the SCR 21 and is sufficient to turn on the SCR, i.e., suificient to cause the SCR to conduct current. Almost instantaneously, capacitor 20 discharges through the winding 10 via the SCR, thereby applying a high voltage pulse of short duration to the winding. This pulse produces a large force on the solenoid armature at a time when it is most needed, i.e., when the air gap in the magnetic circuit of the solenoid is a maximum. After the armature seats, normal operating voltage for maintaining it seated is supplied by the rectifier 15.

The halt-wave rectifier 22 conducts current only during every other half-cycle of the power source, say during each positive half-cycle. It is only during the positive half-cycles, therefore, that the SCR 21 is conditioned to be turned on (and will be turned on if a sufficient voltage is applied to its gate 24). During the alternate or negative half-cycles, the polarity of the SCR is reversed due to the rectified, filtered voltage supplied by winding 13, rectifiers 15, and capacitor 17, and it will not conduct current. It will been seen, therefore, that after the SCR is turned on, whereupon the capacitor 20 discharges through the winding 10, during the negative half-cycle of need for additional components to turn oif the SCR. the SCR will automatically turn off since its polarity is reversed. Thus, switching is accomplished without the need for additional components to turn 01f the SCR. During following positive half-cycles of the power source, the SCR will not be turned on since insufficient voltage is induced in the control winding 25 while the winding 10 remains energized and the armature seated. After the SCR turns off, the capacitor 20 is recharged by the secondary 14 in preparation for the next actuation of the solenoid.

When the winding 10 is to be deenergized, the switch 16 is opened. A diode 26, shunted across the winding 10, is arranged to pass current in the direction of the junction 27 between the SCR 21 and the winding 10. This diode prevents the build up of a reverse voltage in the winding 10 which would normally be created when the switch 16 is opened. Consequently, build up of an induced reverse voltage in the control winding, which would damage the gate 24 of the SCR, is prevented. Another diode 28 is located in the line between the secondary 13 and the winding 10, and is arranged to pass current in the direction of the junction 27. This diode insures that when the capacitor 20 discharges, all the current flows into the winding 10 and no current flows to the secondary 13 or rectifier 15.

From the above description, it will be appreciated that ,4 the present invention provides an actuating circuit which is highly efficient since the only power drawn by the circuit after the armature seats is that sufiicient to maintain the armature in seated condition. In addition, frequent cycling can be accomplished because capacitor 20 receives charge during all the time that it is not actually discharging. Charging continues whether or not the winding 10 is energized. The discharge period of the capacitor 20 is measured in milliseconds. Therefore, even if the winding 10 is energized every few seconds, almost the entire period of each cycle would be available for charging the capacitor.

The invention has been shown and described in preferred form only, and by way of example, and many variations may be made in the invention which will still be com-prised within its spirit. It is understood, therefore, that the invention is not limited to any specific form or embodiment except insofar as such limitations are included in the appended claim.

What is claimed:

In an electric circuit for controlling the operation of an electromagnetic device including a main winding and an armature movable upon magnetization of the device from one position to another, a primary power supply for supplying DC. power to the main winding and having a maximum power value substantially equal to the steady state power required by the main winding for keeping the armature in its energized position, a capacitor, an auxiliary A.C. power supply connected across said capacitor and having a maximum power value greater than said primary power supply, said capacitor being charged by said auxiliary power supply, a control winding inductively coupled with said main winding, and a silicon controlled rectifier arranged in a series circuit with said main winding and capacitor, said control winding being connected to the gate of said silicon controlled rectifier, one

side of said SCR being connected to said A.C. power supply through a half-wave rectifier and the other side being connected to said D.C. supply, whereby when said primary power source is connected to said main winding a current will be induced in said control winding causing said silicon controlled rectifier to conduct and allowing said capacitor to discharge through said main winding, said silicon controlled rectified thereafter automatically having its polarity reversed so that it becomes non-conducting and permits said capacitor to be recharged.

References Cited by the Examiner UNITED STATES PATENTS 2,922,086 1/1960 Stidger 317151 3,143,668 8/1964 Bloodworth et al.

3,154,725 10/1964 Kadah 317l55.5 3,231,786 l/1966 Felcheck 317--l48.5

MILTON O. HIRSHFIELD, Primary Examiner.

SAMUEL BERNSTEIN, Examiner.

R. V. LUPO, Assistant Examiner. 

